Artificial impedance for telephone repeaters



June 9, 1931. M. LEBEDlNSKY 1,809,484

ARTIFICIAL IMPEDANCE FOR TELEPHONE REPEATERS Filed July 25. 1929 Fl'gJ EQUILIBRATING NETWORK ARTIFICIAL IMPEDANCE 411- feaealrg,

lNve/v 771g Patented June 9, 1931 use STATES PATE SN Pica MYRON LEBEDINSKY, OF PARIS, FRANCE, ASSIGNOR T'O GRAMIVIONT, OF PARIS, FRANCE, A CORPORATION OF FRANCE ARTIFICIAL IMPEDANCE FOR TELEPHONE REFEATERS Application filed July 25, 1929,

S jwO' wherein R is the resistance,

L is the inductance,

S is the insulation,

Q s the c apac1ty,

w=21rf, f being the frequency.

My invention has for its object a device producing only a negligible damping, disposed at the repeater station and adapted to equalize for all frequencies the impedance of the station and that of the wire section leading thereto; this device comprises chiefly a condenser inserted in a shunt connecting the two wires, in which latter are inserted induction coils some of which are shunted by condensers. I

Experience has shown that the tuning of the condenser thus connecting in shunt the two wires in a device according to the invention allows the shape of the initial sending end-impedance curve of the device to be varied so that it can be made parallel to the same curve relating to the line; it is then easy, by a proper determination of the input transformer, to cause both curves to coincide, whereby the phenomena of resonance are suppressed.

The following description and appended drawings show by way of example several forms of execution of my invention.

Fig. 1 shows diagrammatically a repeater station provided with two vacuum tubes and Serial No. 380,977, and in France November 24, 1928.

with differential transformers of the known v type and'to which my invention has been adapted. 1

Figs. 2 and 3 show diagrammatically two forms of execution of the device.

On Fig. 1 one of the sections 1 ofthe line is shown connected to one of the windings 2 ofthe transformer 3; the second winding 4- is connected with the differential transformer 5 closed in the well-known manner, over an artificial equilibrating line or network 6. To the middle points 8 and 9 of the windings of this transformer are connected wires leading to the primary of the transformer 11 the secondary of which is inserted in the grid circuit of the amplifying vacuum tube 12. At the-middle of the primary of this transformer 11 is inserted at 18 the device preventing distortion as described in my prior Specification Serial No. 262,260 filed July 25, 1929.

The artificial impedance according to my invention is inserted at 14 between the differential transformer 5 and the grid trans.- former 11.

Fig. 2 shows a form of execution of my invention which comprises four induction coils 15, 16, 17, 18 wound over the same core, the

coils 15 and 16 being wound in opposite directions as are also the coils 17 and 18. The coils 16 and 18 are shunted by the condensers 19 and 21 and a condenser 22 is inserted in a shunt connecting the points common to coils 15 and 16 on one hand and coils 17 and 18 on the other.

The coils 15 and 16 are identical'and the magnetic fluxes produced are therefore equal and opposed for equal currents, but part of the current passing through the condenser 22 these fluxes become unequal and thus the coils 15 i1nd 16 act as a single very weak induction coi The same is the case for coils 17 and 18. It is easy to see that thedevice just described may be replaced by the one shown on Fig. l where the four coils are replaced by two coils 23 and 24 shunted by condensers 25 and 26.

It is not altogether necessary for these coils and condensers to be identical and I may even suppress the induction coil 23 and the corresponding condenser 25.

The working of the device is as follows:

The formula giving the initial sending end impedance can be written: Z =a+jb, a and Z) varying with the frequency.

Let us assume now that in a device as represented on Figure l, we have in 22 an adjustable condenser.

If we vary the capacity of said condenser, we can, for each value of said capacity, plot two curves with the frequencies as abscissae and a or b as ordinates.

It is remarkable that, with the devices disclosed in the application, said curves have forms like those obtained for the same curves with different sorts of cables. So it is possible, by convenient adjustment of condenser 22, to cause the two curves of the repeater to become parallel to the corresponding curves of the section of cable connected with it. By proper determination of the input transformer ratio, it is then possible to cause such curves to coincide.

Of course, the curves are plotted once for all in the laboratory, and then, knowing the features of the section of line, we may, only by examination of said curves, determine the input transformer ratio of transformation and the capacity of condenser 22 which shall avoid resonance.

What I claim is:

1. In a telephonic circuit, the combination of a repeater, a transformer at the input side of said repeater, double wire connections therefor, a grid transformer forming part of the repeater, double means connecting the transformer and the grid transformer two opposed induction coils inserted in each of said means, a condenser shunting one of the coils of each connecting means, a Wire connecting points in each connecting means between the corresponding coils and a condenser inserted in said wire.

2. In a telephonic circuit, the combination of a repeater, a transformer at the input side of said repeater, double wire connect-ions therefor, a grid transformer forming part of the repeater, double means connecting the transformer and the grid transformer, an induction coil inserted in each of said means, condensers shunting the coils, a wire connecting the two connecting means between points on the same side of the corresponding coils and a condenser inserted in said wire.

In testimony whereof I have aflixed my signature.

MYRON LEBEDIN SKY. 

